"If the situation with the coach is not resolved, I could leave Zenit in January," Hulk was quoted as saying by local media. "Everything is possible."

Moscow: Russian champions Zenit St Petersburg, rocked by a players dispute after the big money signing of Hulk, are facing a fresh headache after the Brazilian striker was substituted in a Champions League clash.

Zenit's Italian manager Luciano Spalletti brought off Hulk for midfielder Konstantin Zyryanov with 10 minutes to go in the match against AC Milan on Tuesday.

The Russian champions were leading 1-0 when Spalletti decided to defend the lead and strengthen the back line. But the decision angered the 26-year-old forward, who refused to shake hands with Spalletti as he left the field.

After the match Hulk said he was upset by the decision and threatened to quit if the situation was not resolved.

"If the situation with the coach is not resolved, I could leave Zenit in January," Hulk was quoted as saying by local media. "Everything is possible."

Spalletti dismissed rumours that he was at loggerheads with Hulk, adding that he had the backing of Alexei Miller, the chief of Zenit's general sponsor, Russian gas giant Gazprom.

"Great footballers are always upset after the manager substitutes them," Spalletti said. "Meanwhile, Miller has sent me an SMS message. He congratulated me and wrote that he approved all of my substitutions."

Zenit failed to progress to the Champions League quarter-final stages but the victory secured them a berth in the Europa League.

The club have only recently recovered from a spat between club officials and Russia captain Igor Denisov, who demanded a pay rise after Hulk's annual salary of six million euro became known.

Midfielder Denisov was demoted to Zenit's youth team and only returned to the first team after six weeks out in the cold after apologising publicly to club bosses and Spalletti.

His demands were also reportedly supported by Russian international forward Alexander Kerzhakov, who was also sent to practice with the youth team for a week.